Introduction to particle accelerators

Walter Scandale

CERN - AT department

Roma, marzo 2006

Lecture VI - neutrino projects

topics Superbeam & Neutrino Factory & Muon Collider

Target

Proton driver

Scenarios for Neutrino beams

The basic blocks– Proton driver 1 to 4 MW– Muon accelerator - Muon storage ring (decay ring / collider)

This suggests (at least) 3 stages towards a neutrino factory:1. Neutrino superbeam from pion decay with uo to 4 MW proton

driver. (Stages 1a, 1b, 1c might be 1, 2, 4 MW proton driver performance.)

2. Add a muon capture channel + a muon accelerator 3. Add a storage ring to produce muon decay neutrinos F (3a)

and a collision storage ring (3b)

Neutrino Beams:– Superbeam neutrinos from π± -> ± + (anti ) . (Pions from pA -> π±X.)– Factory neutrinos from ± -> e± anti e ( anti e). (Muons from π± -> ± + (anti ) )– -beam neutrinos from 6He -> 6Li e- anti e, 18Ne -> 18Fe+ e

Components of a Neutrino Factory

I > 1 x 1020 µ decays / year @

one s.s.

Proton Driver— primary beam on production target

Target, Capture, Decay— create π, decay into µ

Bunching, Phase Rotation— reduce ∆E of bunch

Cooling— reduce transverse emittance

Acceleration— 130 MeV ==> 20 GeV

Decay Ring— store for ~500 turns; long straigth section

Driving issues of a Neutrino Factory

Constructing a muon-based F is challenging

— muons have short lifetime (2.2 µs at rest) puts premium on rapid beam manipulations

– requires high-gradient RF for longitudinal cooling (in B field)

– requires presently untested ionization cooling technique

– requires fast acceleration system

— muons are created as a tertiary beam (p==> ==> µ) low production rate

– target that can handle multi-MW proton beam large muon beam transverse phase space and large energy spread – high acceptance acceleration system and storage

ring

— neutrinos themselves are a quaternary beam even less intensity and “a mind of their own”

— developing solutions requires substantial R&D effort R&D should aim to specify:

– expected performance, technical feasibility/risk, cost (matters!)

Examples of Neutrino Factories

KEK scheme

To Far

Detector

2

FFAG I(3-8GeV)

(

FFAG II(8-20GeV)

FFAG III(20-50GeV)

Far Detector 1Far Detector

2

Neutrino Factory

Near Detector

R109

To Far Detector 1

Muon Decay Ring

The UK scheme

The Super Beam

Neuffer and Palmer (1995) suggested that a high-luminosity muon collider might be feasible

Neutrino Factory and Muon Collider Collaboration started in 1995 has since grown to 47 institutions and >100 physicists

Snowmass Summer Study (1996) study of feasibility of a 2+2 TeV Muon Collider [Fermilab 1996]

First neutrino Factory suggested by Geer (1997)

A brief history of the Neutrino Factory

Muon storage ring is an old idea: Charpak et al. (g – 2) (1960), Tinlot & Green (1960), Melissinos (1960)

muon colliders suggested by Tikhonin (1968) but no concept for achieving high luminosity until ionization cooling suggested by O’Neill (1956), Lichtenberg et al. (1956),

muon ionization cooling proposed by Skrinsky & Parkhomchuk (1981) and Neuffer(1979, 1983)

The piece of cake: the ionization cooling

Energy loss dE/dx

Momentum recovery though RF

- RF cavities between absorbers replace E –> Net effect:

reduction in p at constant p||, i.e., transverse cooling.

- Reduce heating by Coulomb scattering: Strong focusing (small ß along the channel) Large radiation length Xo (low-Z absorber)

High field solenoid / lithium lens

€

Eμ → Eμ −dEμ

dsΔs

θ →θ + θ rms along Δs

⎧

⎨ ⎪

⎩ ⎪⇒

dεN

ds= −

1

β 2

dEμ

ds

εN

Eμ

+β⊥ 0.0014GeV( )

2

2β 3Eμ mμ LR

Absorber Accelerator

Momentum loss is opposite to motion, p, p x , p y , Edecrease

Momentumgainispurelylongitudinal

Largeemittance

Smallemittance

Figure of merit:M = LR dE/ds

RF cavity

Ionization cooling test experiment: MICE

Ionization cooling is a brilliantly simple idea!• BUT: never observed experimentally delicate design and engineering problem a crucial ingredient in the cost and performance optimization

Goals of MICE: design, engineer and build a section of cooling channel giving the desired performance for a F;

use a beam and measure the cooling performance.

Muon storage rings and Neutrino Factories may be the best way to study neutrino mixing and CPV

F technical feasibility has been demonstrated “on paper”

We need the experimental demonstration of muon ionization cooling feasibility & performance

MICE Proposal approved and Phase 1 funded Scope and time-scale comparable to mid-sized HEP experiment

I guess there’ll always be a gap between science and technology

Status of MICE

Progress of MICE

Focusing solenoid

Cavity prototypeDecay channel and its solenoid

Final spectrometer

Ionization cooling: B-flip of solenoidTo get low ß and hence to produce small emittanceuse a big S/C solenoids & high fields! ==> expensive

envelop

Ionization cooling: alternative lattices

Alternating gradient allows low with much less superconductor

Lattice design questions Many alternative configurations1.Alternating solenoid2.FOFO3.Super-FOFO4.(+ RFOFO, 5.DFOFO, 6.Single-Flip,

7.Double-Flip) —both with cooling and non-cooling

==> arrive at baseline specifications

end-to-end simulations— correlations in beam and details of distributions have significant effect on transmission at interfaces (muons have “memory”)

— simulation effort will tie all aspects together

Transverse ionization cooling self-limiting due to longitudinal emittance growth, leading to particle losses

straggling plus finite E acceptance of cooling channel need of longitudinal cooling for muon collider; could also help for F

Possible in principle by ionization above ionization minimum, but inefficient due to straggling and small slope d(dE/ds)/dE

Longitudinal cooling ?

Neutrino factory based on extreme cooling

“extreme cooling” via emittance exchange in helical focusing channel filled with dense low-Z gas or liquid proposed by R. Johnson, Y. Derbenev, et al. (Muons, Inc.)

prototype helical solenoid+rotating-dipole +quad magnet from AGS “Siberian Snake”

Ecm = 5 TeV<L> ~ 5·1034 cm-2s-1

µ–: 6 – 11 GeVµ+: 9 – 19 GeV

µ production

4-MW Proton Beam on target 10-30 GeV p-beam appropriate for both Superbeam and Neutrino Factory.

⇒ 0.8-2.5 ×1015 pps; 0.8-2.5 ×1022 protons per year of 107 s. Rep rate 15-50 Hz at Neutrino Factory, as low as 2 Hz for Superbeam.

⇒ Protons per pulse from 1.6 ×1013 to 1.25 ×1015.⇒ Energy per pulse from 80 kJ to 2 MJ.

Small beam size preferred:≈ 0.1 cm2 for Neutrino Factory, ≈ 0.2 cm2 for Superbeam.⇒ Severe materials issues for target AND beam dump.

Critical issues Radiation Damage - Melting - Cracking (due to single-pulse “thermal shock”).

Optimum target material— solid or liquid— low, medium, or high Z

Intensity limitations— from target— from beam dump

Superbeam vs. Neutrino Factory trade-offs— horn vs. solenoid capture— can one solution serve both needs?— is a single choice of target material adequate for both?

Is there hope for a 4 MW target ? Several “smart” materials or new composites should be considered:

— new graphite grades— customized carbon-carbon composites— Super-alloys (gum metal, albemet, super-invar, etc.)

While calculations based on non-irradiated material properties may show that it is possible to achieve 2 or even 4 MW, irradiation effects may completely change the outlook of a material candidate.

ONLY way is to test the material to conditions similar to those expected during its life time as target.

Target / capture / decay

For secondary pions with Eπ <∼ 5 GeV (Neutrino Factory), a high-Z target is favored,

but for Eπ >∼ 10 GeV (some Superbeams), low Z is preferred.

Horns

Carbon composite target with He gas cooling (BNL study):

Mercury jet target (CERN SPL study):

Palmer (1994) proposed a solenoidal capture system for a Neutrino Factory. Collects both signs of ’s and ’s, Solenoid coils can be at some distance from proton beam.

⇒ ≥ 4 year life against radiation damage at 4 MW.⇒ Proton beam readily tilted with respect to magnetic axis.⇒ Beam dump out of the way of secondary ’s and ’s.

Mercury jet target and proton beam tilt downwards with respect to the horizontal magnetic axis of the capture system

The mercury collects in a pool that serves as the beam dump (F) .

⇒ Point-to-parallel focusing for

⇒ Narrowband neutrino beams (less background)

€

Pπ =eBd

2πc 2n +1( )

€

Eν ≈ 12 Pπ =

eBd

2πc 2n +1( )

Solenoids

Solenoidal capture magnet (≈ 20 T) with adiabatic transition to solenoidal decay channel (≈ 1 T).

€

ΦB = BR2 = in var iant

R∝p⊥B

⇒ ⎧ ⎨ ⎪

⎩ ⎪

p⊥2

B= in var iant ⇔ p⊥, final = p⊥,initial

Bmin

Bmax

1-cm-diameter Hg jet in 2e12 protons at t = 0, 0.75, 2, 7, 18 ms (BNL E-951, 2001).

Liquid target/dump using mercury, or a Pb-Bi alloy. ⇒ F≈ 400 J/gm to vaporize Hg (from room temp),⇒ Need flow of > 104 g/s ≈ 1 l/s in target/dump to avoid boiling in a 4-MW beam.Energy deposited in the mercury target (and dump) will cause dispersal, but at benignvelocities (10-50 m/s).

Liquid / solid target

Solid Targets (Superbeams)

alternativeA solid, radiation-cooled stationary target in a 4-MW beam will equilibrate at about 2500 C. ⇒ Carbon is only candidate(in He atmosphere to suppress sublimation.)

A moving band target (tantalum) could be considered in a toroidal capture system

Muon production based on FFAG

FFAG Magnetscaling

KEK

Osaka Univ.

Proton driver for a Neutrino Factory

Proton Driver Questions Optimum beam energy

— depends on choice of target ==> consider C, Ta, Hg

Hardware options— FFAG, linac, synchrotron ==> compare performance, cost

Beam dynamics– beam current limitations (injection, acceleration, activation)

– bunch length limitations and schemes to provide 1-3 ns bunches, approaches for bunch compression

– repetition rate limitations (power, vacuum chamber,…)

– tolerances (field errors, alignment, RF stability,…)

Superbeam versus Neutrino Factory Factory requirements

- required emittance and focusing

- staging

Intensity history of multi-GeV proton accelerators.The numbers in parenthesis indicate the typical repetition rate.

€

P = E × I = E ⋅ Ipeak ⋅DF

Proton drivers

High proton beam power machines presently operating, under construction, or planned

Existing and Proposed Proton Drivers

driver powe r type ene r gy f r equ e ncy ppp Pulse

st r uctu r e [MW] [GeV] [Hz] [10 13] tp

[ms] Nb tb

[ns] BNL-AGS 1 Synch 28 2 .5 9 720 24 3 4 Synch 28 5 18 720 24 3 4 Synch 40 5 12.5 720 24 3 FNAL 2 Synch 1 8 15 10 1.6 84 1 2 Linac2 8 10 15

FNAL MI 2 Synch 120 0 .67 15 10 530 2 CERN SPL 4 LAR 2.2 50 23 3 .2 140 1 4 LAR 3.5 50 14 1.7 68 1 J-PARC 0.75 Synch 50 0 .3 31 4 .6 8 6 RAL 4 Synch 5 50 10 1.4 4 1 4 Synch 6–8 50 8 .3 1.6 6 1 4 FFAG 10 50 5 2 .3 5 1 4 Synch 15 25 6 .7 3 .2 6 1 RAL/CERN 4 Synch 30 8 .33 10 3 .2 8 1 KEK/Kioto 1 FFAG 1 104 0 .06 0 .4 10 10 1 FFAG 3 3103 0 .06 0 .5 10 10

The pulse structure is given in terms of the pulse duration tp, the number of bunches Nb making up each pulse, and the final compressed rms bunch length tb.

Two rings each, stacked vertically

180 MeV, 280 MHz H- Linac

Two 25 Hz Rapid Cycling Synchrotrons,

4 bunches in each. Energy 1.2 GeV to 5 GeV.

Bunch compression to 1 ns rms at pion target

Achromat for momentum and betatron

collimationTwo 50 Hz Rapid Cycling Synchrotrons, with two bunches of 2.5 1013 protons in each.

Energy 180 MeV to 1.2 GeV

Momentum ramping

Mean radius 65m

Driver I: 4 MW, 50 Hz, 5 GeV

Driver II: 4 MW, 25 Hz, 15 GeV

Two 12.5 Hz Rapid Cycling Synchrotrons,

6 bunches in each. Energy 3 GeV to

15 GeV. Bunch compression to 1 ns

rms at pion target

Two 25 Hz Rapid Cycling Synchrotrons, with three bunches of

1.11 1013 protons in each.

Energy 180 MeV to 3 GeV

180 MeV, 280 MHz, H- Linac

Two rings each, stacked vertically

Achromatic arc for collimation

Momentum ramping

Mean radius 150m

Large aperture magnets and much higher RF voltages per turn due to a low energy injection and a large and rapid swing of the magnetic field,

Field tracking between many magnet-families under slightly saturated conditions,

RF trapping with fundamental and higher harmonic cavities, H- charge stripping foil, Large acceptance injection/dump/extraction section, Ceramic chambers, Beam instabilities, Comparison with full-energy linac+storage ring approach from view point of the radiation protection.

Challenges of the RCS

20 ÷ 25 kV/m cavity

Type of accelerator Energy [GeV]

duty factor DF

Neutron for material studies• neutron yield proportional to beam power

0.5 ÷ 10

CW ÷ 10-4

Neutron spallation | nuclear waste transmutation | accelerator driven supercritical reactors• lower energy to limit the power deposition in the target window• higher energy up to full absorption of beam power in the reactor vessel

0.5 ÷ 5 CW

Kaons and heavy flavor• high DT to minimize the detector dead time• high energy to stay beyond production threshold

> 20 0.5 ÷ 1

Neutrino• low DF to minimize background from cosmic rays• energy tailored on wanted neutrino energy

> 1 GeV 10-5

Muons for neutrino factory• low DF to limit the up-time of muon cooling channel

• high E to minimize the peak current (eg for 5MW ==> Ipeak ~ 150 A)

> 3 GeV 10-5

Muons for muon colliders• low DF to minimize the muon bunch length (hence maximize the luminosity)

• high E to minimize the peak current (eg for 5MW ==> Ipeak ~ 2kA

20 ÷ 30 10-7

Other applications of Proton Drivers

The -beam concept-beam Piero Zucchelli• A novel concept for a neutrino factory: the beta-beam, Phys. Let. B,

532 (2002) 166-172.

ADVANTAGES OF BETA-BEAMS :

Pure ( or ) beams.

Well known neutrino fluxes.

Strong collimation.

Lorentz boost

high

A NOVEL METHOD TO PRODUCE INTENSE,

COLLIMATED, PURE HIGH ENERGY e BEAMS FROM BOOSTED RADIOACTIVE IONS.

CONVENTIONAL METHODS :

Neutrino beams are produced using the decay of pions and muons.

CERN: -beam baseline scenario

B = 1500 TmB = 5 TLss = 2500 m

€

26He→3

6Li e−ν

Average Ecms =1.937 MeV

1018Ne→ 9

18Fe e+ν

Average Ecms =1.86 MeV

ECR

PS

Decay

RingSPS

ISOL target & Ion source

SPL

Cyclotrons, linac or FFAG

Rapid cycling synchrotron

Nuclear Physics

An annual integrated flux of 2.9*1018 anti-neutrinos (from 6He at =100) 1.1*1018 neutrinos (from 18Ne at g=100)

With an Ion production in the target to the ECR source: 6He= 2*1013 atoms per second 18Ne= 8*1011 atoms per second

CERN: -beam baseline limitations

Isotope production

The self-imposed requirement to re-use a maximum of existing CERN infrastructure

– Cycling time, aperture limitations, collimation systems etc.

The high intensity ion bunches in the accelerator chain and decay ring

– Space charge

– Decay losses

6He 18Ne

Decay ring [ions stored]

9.7*1013 7.5*1013

SPS ej [ions/cycle] 9. 0*1012

4.3*1012

PS ej [ions/cycle] 9.5*1012 4.3*1012

Source rate [ions/s]

2*1013 2*1013

Typical intensities of 108-109 ions for LHC injector operation (PS and SPS)

Decay ring design aspects

The ions have to be concentrated in a few very short bunches– Suppression of atmospheric background via time structure.

There is an essential need for stacking in the decay ring

– Not enough flux from source and injector chain.

– Lifetime is an order of magnitude larger than injector cycling (120 s compared with 8 s SPS cycle).

– Need to stack for at least 10 to 15 injector cycles. Cooling is not an option for the stacking process

– Electron cooling is excluded because of the high electron beam energy and, in any case, the cooling time is far too long.

– Stochastic cooling is excluded by the high bunch intensities.

Stacking without cooling “conflicts” with Liouville

reminder Neutrino physics is very appealing Neutrino beam devices are complex and expensive Superbeam is the basic initial block os a modern neutrino facility, it relies on the construction of a multimegawatt proton driver

Muon accelerators are the next step and rely on a performing target system capture channel and on the very challenging ion cooling

Neutrino factories and muon muon colliders are the last step (cost is matter

Beta-beams are a clever shortcut

Lecture VI - neutrino projects